This invention relates to the franking of mail items by accounting for postage charges in respect of those items and printing an impression on each item to indicate that a postage charge has been levied. In particular it relates to the use a general purpose computer in combination with secure means for carrying out franking of mail items.
It is known to use postage meters to print franking impressions on mail items to indicate that the postage charges for those items have been accounted for. Known postage meters are designed specifically to carry out functions required in respect of franking mail items. Current electronic postage meters include electronic circuits to carry out accounting and control functions and printing means operated by the electronic circuits to print postage information on mail items. The electronic circuits include memories to store accounting data, the memories generally include a descending register to store a value of credit available for use in franking mail items, an ascending register for storing an accumulated value of postage charge used by the postage meter in franking mail items and an items register for storing a count of the number of mail items on which postage data has been printed by the postage meter in franking those items. The memories are non-volatile so that in the event of interruption of the supply of power to the postage meter, due for example to a fault or power down of the postage meter, the accounting data is retained and not lost.
In order to provide verifiable storage of the accounting data, it has been customary to provide a plurality of replications of the registers in the memories and for example usually two separate memory devices are provided and two of each register is provided in each memory device. Thus in the event of a fault occurring in one of the registers resulting in corruption of data stored in that register, the data can be ascertained from the other copies of that register. During operation of the postage meter in carrying out a franking operation, the accounting circuits check that the data content of all replications of each register are in agreement and, in the event that the data in any replication of a register is inconsistent with data in other replications of that register, the accounting circuits cause inhibition of use of the postage meter for franking operations. Continued use of the postage meter is possible only after examination and correction of the data by an authorised person.